1. Field of the Invention
The invention relates to a drive unit which is provided for each driving wheel of a vehicle and can apply driving force or braking force by transmitting power directly to the driving wheel for which it is provided, as well as a control apparatus that controls that drive unit.
2. Description of the Related Art
Japanese Patent Application Publication No. 2007-99106 (JP-A-2007-99106) describes one example of a so-called in-wheel motor (IWM) drive unit that has been developed, in which a motor is arranged in or near a wheel of the wheel/tire assembly and is used M directly drive that wheel/tire assembly. The in-wheel motor drive unit described in JP-A-2007-99106 includes a motor, a planetary reduction gear, an output shaft, and a wheel rim. At least one bearing that rotatably supports a rotating element of the planetary reduction gear which is connected to the output shaft is arranged to the inside, in the vehicle width direction, of the center plane in the width direction of the wheel rim, and the output shaft is rotatably supported by this bearing. The motor, the planetary reduction gear, the output shaft, and the wheel rim are all connected together in that order so that power can be transmitted among them. Therefore, output torque of the motor can be transmitted from the motor to the wheel rim while being increased.
An in-wheel motor drive unit such as that described in JP-A-2007-99106 has a motor as a driving power source arranged in or near the wheel of the wheel/tire assembly, which transmits power directly to the wheel/tire assembly. This obviates the need to provide a power transmitting device such as a transmission or a differential in the vehicle, thereby enabling the structure of the vehicle to be simplified. On the other hand, because power is transmitted directly between the drive unit and the wheel/tire assembly, it is possible that an unexpectedly large external force may be directly transmitted from the wheel/tire assembly side to the drive unit at times such as when the vehicle is traveling on a rough road with potholes, bumps, or obstacles or the like, for example, which may damage the drive unit.
One conceivable way of dealing with unexpected excessive external force from the wheel/tire assembly side is to provide a greater safety margin and increase the strength of the various components that receive the external force such that even if such unexpected excessive external force is input to the drive unit from the wheel/tire assembly side, for example, it will not cause an abnormality in a driving shaft, gears or the motor in the drive unit. In this case, the various components are made larger or of stronger material than they are when they are designed without taking unexpected excessive force such as that described above into account. However, this may increase the size and weight, or manufacturing costs of the drive unit.